1. Field of the Invention
This invention relates to a novel lubricant film to be formed on the surfaces of sliding metal parts under high surface pressure for preventing galling thereof.
2. Description of the Prior Art
Galling occurs to metal surfaces which are in sliding contact under high surface pressure, particularly in a case where the metal has low thermal conductivity and a large thermal expansion coefficient like stainless steel, often causing problems in various industrial machines.
For example, if the phenomenon of galling occurs when connecting threaded ends of oil well pipes, the connecting and breaking operation has to be interrupted to lift up the pipe, cutting off the defective pipe end, and tapping a fresh screw thread on the pipe end, wasting considerable time and labor. In addition to oil well pipes, the same applies to the metallic sliding parts which are subjected to a high surface pressure.
There have thus far been developed various lubricants for preventing galling of metallic sliding parts, which in most cases contain a solid lubricant, a lubricant additive and/or an organic resin. For example, a lubricant of MoS.sub.2 -resin system is proposed in U.S. Pat. Nos. 3,051,586, 4,303,537, 3,146,142 and 4,206,060 and Japanese Patent Publication No. 51-43558, a lubricant of MoS.sub.2 -Sb.sub.2 O.sub.3 -resin system is disclosed in U.S. Pat. Nos. 3,314,885 and 3,882,030, and Kirk-Othmer Encyclopedia of Chemical Technology, and a lubricant of graphite-resin system is described in U.S. Pat. No. 2,335,958.
In order to make the most of the functions of the component of a lubricant and to maintain satisfactory lubricative properties in severe conditions under a high surface pressure, the type of lubricant and blending ratios of the ingredients are important factors which should be taken into consideration. The lubricant of the above-mentioned systems or compositions are not necessarily satisfactory as a lubricant for sliding metal parts under high surface pressure and cannot be expected to sufficiently prevent galling.